Mechanical jar

ABSTRACT

An illustrative embodiment in accordance with the present invention in jars includes a mandrel and housing which are telescopically disposed and adapted for connection in a pipe string, said mandrel and housing having spaced impact surfaces which can be brought together to deliver a jarring blow, an expansible sleeve member having threads meshed with threads on said mandrel, cam surfaces on said threads for expanding said sleeve member and releasing said threads from mesh with one another, means released by longitudinal relative movement between said housing and said sleeve member for locking said sleeve member in threaded engagement with said mandrel; and a resilient column structure coacting between said housing and said sleeve member for yieldably resisting longitudinal relative movement so that a force of a predetermined magnitude can be applied to said housing before said threads are permitted to release.

United States Patent- Kisling, III

54 MECHANICAL JAR [72] Inventor: JamesW, Kisling IlI, Houston,

Tex. 73 Assignee: Schlumberger Technology Corporation, New York, NY.

22 Filed: Oct. 20, 1970 21 Appl.No.: 82,284

[52 us. c1 ..175/304,175/302 [58] FieldofSearch ..175/293,298, 300, 302,303, 175/304, 299-, 166/178 [56] References Cited UNITED STATES PATENTS2,008,765 7/1935 McCullough ..175/304x 2,016,607 10/1935 McCullough..175/302 2,059,540 11/1936 Stephan ..175/304x 2,618,466 11/1952Bagnelletal ..175/298 2,618,467 11/1952 Bagnelletal ..175/298 2,621,02512/1952 Denning ..175/304 2,978,048 4/1961 Walker ..175/299x 3,050,1318/1962 Siracusa ..175/303x 45 Aug. 22, 1972 Primary Examiner-David H.Brown Attorney-Emest R. Archambeau, Jr., Stewart F. Moore, David L.Moseley, Edward M. Roney and William R. Sherman [57] ABSTRACT Anillustrative embodiment in accordance with the .present invention injars includes a mandrel and housing which are telescopically disposedand adapted for connection in a pipe string, said mandrel and housinghaving spaced impact surfaces which can be brought together to deliver ajarring blow, an expansible sleeve member having threads meshed withthreads on said mandrel, cam surfaces on said threads for expanding saidsleeve member and releasing said threads from mesh with one another,means released by longitudinal relative movement between said housingand said sleeve member for locking said sleeve member in threadedengagement with said mandrel; and a resilient column structure coactingbetween said housing and said sleeve member for yieldably resistinglongitudinal relative movement so that a force of a predeterminedmagnitude can be applied to said housing before said threads arepermitted to release.

13 Claim, 7 Drawing Figures Patented Aug. 22, 1972 3,685,599

3 Sheets-Sheet 1 F G. 7. I

33 2 i i I x P i E 32 i I3- 1 E w s I A l James W Kisling,1F INVENTOR AHORNE Y Patented Aug. 22, 1972 Ja mes W KislingJZT :5 Sheets-Sheet zFIG.2B

Fl INVENTOR BY Xflud/flA 7 ATTORNEY Patented Aug.. 22, 1972 3,685,599

5 Sheets-Sheet 5 James w. KislingJH INVENTOR ATTORNEY 1 MECHANICALJARThis invention relates generally to well jars used to extricate stuckobjects from well bores, and more specifically to a new and improvedmechanical jar hav- 1 ing a tripping or release mechanism that isconstructed Y and arranged to be wear resistant during long" con- Itinued usage. A

When drilling boreholes through earth 7 formations where sticking'is aproblem, mostdrillers will tuna jar in the drill string. A jar is adevice having telescoping members with spaced apart impact surfaceswhich can be brought together in a violent manner in order to deliver ajarring blow to 'a stuck tool with the hope of freeing it. The jarincludes a tripping mechanism that functions to prevent telescopingmotion" until a predetermined release force has been applied to thedrill string, the force causing the drill string to' stretch and storeenergy. When. the tripping mechanism releases, the drill stringcontracts and causes the jar to hit and deliver a considerable impactforce to the stuck tools. Usually, the jar must be operated many timesbefore the stuck tools are driven free, and in fact circumstancesrequiring many hours of continuous jarring are not uncommon. a

A number of the problems associated with prior art.

itself 'due to excessive stress and loading applied to the" partsthereof. In any event, because of the environmental in which a jarmustfunction, such devices must be extremely rugged in order to remainoperational.

One object of the present. invention is to provide a new and improvedwell jar apparatus having-a tripping or release mechanism which is.adapted to be extremely rugged and wear resistant. v

Another object of the present invention is to provide a new and.improved jar apparatus havinga' substantially constant and predictablerelease force for an extended period of time of use. These and otherobjects are attained with the concepts of the present invention by a jarapparatus comprising telescopically disposed mandrel I and housingmembers adapted for connection in a drill however expansion is preventedby locking surfaces on the sleeve member and the housing, the lockingsurfaces being releasable by longitudinalmovement of the housing alongthe sleeve member. The use of threads as above mentioned provides a newand improved structure which distributes applied. loads over aconsiderable drilled throughearthformationsbyusing conventional. rotarydrilling techniques. A drill bit l liis attached to the lower end of'adrill string which normally-includes a in accordance nermost element andthe outermost element placesalconnection with the followingdetaileddes'criptionjof 3 an'embodiment taken'in conjunction withtheaplength of area to maintain compression stresses withinacceptablelimits, thereby keeping wear on thetripping mechanism to a minimum andproviding a jar having a substantially constant release force over anextended period oftimeofuse. I

In order to enable'energy tobe stored in the drill stringby stretching"it before the tripping mechanism releases, a resilient structureisdisposed in opposition to the longitudinal movement required todisengage the lockingsurfaces on the housing and'the sleeve member..

In accordance with fa preferred embodiment 'of the present invention,the resilient structure, includes a plurality of concentrically disposedtubular elements having altemate opposite ends coupled to one another insuch a manner that oppositely disposed force on the internate elementsin compression and tension."llius the composite structure is in the.nature of a short "column having aver y high modulus of elasticity, theone or more "elements that" arein tension also providinga degree oflateral'support to prevent buckling of those elements having compressionloading.

The present invention has other objects, features and advantages whichwill become more clearly apparent in pended drawings in which:

I FIG. -l'is a somewhat schematic viewjof a drill string and jar in aborehole;

nos. 2A-2C are longitudinal sectional at of the tripp' g mechanismand"associated structure in ac-' cordance with the present invention; rV

FIG. 3 is an isometric view of the tripping sleeve; FIG. 4 is across-section on line 4-4 of FIG. 2B; and

. no. 5 is a longitudinal half-section view'to illustrate keying systemused inthetripping further detail of the mechanism..,

Referring initially to FIG. 1, aboreholelfl is being selectively,coupled at various locations in the drill I string, but is preferablylocated at a point'between the uppermost drill collar andthe drill pipeUnder certain borehole conditions,such as soft orv highly permeableformations, particularly when encountered in v deviated wells, there istherisk that the bit and/or the drill collars may become stuck. Whensuch sticking 'occurs for any reason, the jar 13 can be operated to freeI the stuck tools. I The jar l3 includesv a tubular housing 29 that istelescopically disposed over a tubular mandrel 21, the

ward movement causing one hammer provided-by an anvil" provided by anoutwardly, extending shoulder housing having a threaded box portion 22and the mandrel 21 having a similar portion 23 for coupling the jar inthe drill string; The mandrel 21 has'a central bore 24' which continuesthe drilling fluid circulation path throughthefdrill string. The housing20 is movable to I some extent in both longitudinal directions along themandrel 21 from 'a central or cocked" position, up-

inwardly extending shoulder surface 25 to strike an until the stuckvtools are driven loose.

.26 on the mandrel, downward movement causing another hammer surface 27to strike a second anvil surface 28. vThus the jar" 13 is adapted to hitin. both directions, upward and downward. The impact force in eitherdirection is transmitted bythe mandrel 21 to the longitudinal movementrequired beforedisengagement can occur. The release grooves 48 haveinclined wall v surfaces 49 and 50 in order to provide an. inwardcamming action in the presence of longitudinal force stuck toolstherebelow. The housing and the mandrel 21 have coengaging splines 29for transmitting rotation .through the jar during drilling operations. Aseal packing 30 prevents drilling fluids from entering in between'thehousing 20 and mandrel 21 at their lower ends, whereas a floating orcompensating seal packing unit 31 is used to prevent fluids fromentering at their upper ends. The vacant spaces between the housing 20and the mandrel 21 can be filled a typical lubricatingoilorthelike. v

A tripping mechanism indicated generally at 32 is disposed in betweenupper and lower resilient structures 33 and 34' and functions torestrainlongitudinal' movement of the housing 20 in either directionfrom the cocked or intermediate position to enable energy to be storedin the drill string before the jar hits so that a blow of considerablemagnitude can be struck. Once the tripping mechanism 32 releaseshowever, movement of the housing 20 along the mandrel 21 is unrestrictedas the, hammers approa'chthe respective anvils. After a blow isstruck,the housing 20 i's mov'ed by.

the drill pipe 14 in the opposite direction, and the tripping'mechanism32 is automatically recocked in the intermediate position. The jarn'ngaction is repeated As shown in greater detailin FIG. 2B,

' locking sleeve .45 is alsoslotted-at circumferentiallyspaced locationsto receive outwardly extending projections 54 and 55 formed on dependingportions 56 and 57 of upper and lower drive rings 58 and 59 which on thesleeve member 35 when the threads'47 are meshed with the release groovesj Theupper end ofthe locking sleeve 45 abuts against an inwardlyextending shoulder 51- onv the housing 20, whereas the lower end isengaged by a'bushing 52 that is disposed above an inwardly extendingshoulder 53 (FIG. 2C) on'the housing to fix the lockin g'sleev elongitudinally with respect to the housing. Each end of the are keyed tothe mandrel 21 in a manner and for purposes tobe more fullydescribedbelow. 1 Y

Annular thickened portions60-and 61 :or the mandrel 21 are providedaboveandibelow the threads 37,

the portions having larger lateral dimensions than the height of thethreads, but:are-considerably long with respect to the lead ofthethreads. The sleeve member 35 has similar inwardly-thickened portions62 and, 63 which'engage above and below the respective portions 60,and61 on the mandrel 21. Further, the crests of the threads 37 are formedon a' smaller diameter than the the tripping mechanism 32 includes anexpansible and contractable sleeve r'nember that is normallycontractedaround thev mandrel 21, the sleeve member having internalthreads 36that mesh with companion external threads 37 formed on areduced diameter section of the mandrel. The threads 36 and 37 have astub form providing inclined wall surfaces 39 and 40. When the 'sleevemember 35 and the mandrel 21 are'forced inopposite however, the sleevemember 35 is locked in contracted condition around the mandrel 21 bylocking surfaces '43 (FIG. 28) provided by threads 44 on a lockingsleeve 45, the surfaces slidably engaging like surfaces 46 provided bythreads 47 formed on the exterior of the sleeve member 35. As disclosedin full detail in application, Ser. No. 82287, Berryman, filedconcurrently herewith and assigned to the assignee of this invention,the release grooves'48 formed between the locking surfaces 43iareadapted to receive the threads 47 on the sleeve member 35 upon relativelongitudinal movement of the locking sleeve 45 and the member 35, thuspermitting expansionof the'sleeve member to a condition where thethreads 36 and 37 are disengaged. The

. locking surfaces 43 and 46 extend parallel to theaxis of thesleeve'member 35 and thus positively prevent any outward expansionof thesleeve member during the outer diameter of the mandrel21, whereas thebore size through the sleeve threads 36"is larger than the transversedimension of the portions 60 and 61. Thus, when the sleeve member 35is'permitted to expand and move upwardly, for example, alongthe mandrel21,- the.

- portion 62 will ride along the outer surface 64 or'the -mandrel 21',while .the lower portion 63 will ride first over the outer surface'ofthe lower-mandrel portion 61 and then along the crests of the threads37. The crests of the sleeve member threads 36 will slide along theupper mandrel portion 60, with the result beingfthat the respectivesleeve member and mandrel threads 36 and 37 are positively held out ofengagement as the sleeve member 35 moves relatively along the mandrel 21in either direction.

It will be apparent thatin .order for the sleeve member 35 to bereleased from the mandrel 21 to enable unrestricted telescopingmovementrthe housing 20 and the locking sleeve 45 must move eitherupwardly 1 or downwardly relative to the sleeve member 35. Such relativemovement is restrained however by the resilient structures 33 and 34.Since each structure is madeof identical, oppositely dispowd parts, theupper I structure will be discussed in detail with the appropriatenumbers -referred to in the drawings, the lower resilient structure 34having parts numbered in the same manner but with the prime notation.The upper resilient structure 33 is shown in FIG. 2A as including anouter tube 68, an intermediate tube 69 and an inner tube 70 allconcentrically disposed and made of metallic materials. The intermediatetube .69 has I thickened sections 71 and 72 at its ends, the lowersection providing an upwardly facing shoulder'73 and the upper sectionprovidinga downwardly facing shoulder 74. The lower end of the outertube .68 abuts against the shoulder 73, whereas the upper end of theinner tube abuts the shoulder ,74'. Thus it will be ap-' preciated thatoppositely directed longitudinal'forces applied to the outer tube 68 andthe inner tube 70 will place these tubes in compression and theintermediate tube 69 in tension. The total deflection of the compositestructure of course will be the sum of the respective elongation andforeshortenings of the individual tubes, so that the tubes provide aresilient structure in the nature of a spring having a high modulus ofelasticity. The upper end of the outer tube 68 and the lower end of theinner tube 70 extend beyond the adjacent ends of the intermediate tube69.

The drive rings 58 and 59 are located between the sleeve member 35 andthe respective resilient structures 33 and 34, each drive ring having aninternal annular recess 76 (FIG. 2B) that receives a washer 77. Thewasher 77 has a concave annular groove 78 that receives a rounded end ofa thrust sleeve 79. The other end of each thrust sleeve 79 is alsorounded andis received within an annular groove 80 in the end of thesleeve member 32. Each of the thrust sleeves 79 is also made to beradially expansible and contractable by slots 81 (FIG. 5) extending inalternating longitudinal directions for less than the full lengththereof in the same manner as the slots in the sleeve member 35 shown inFIG. 4. The provision of the slotted thrust sleeves 79 having the samecapability for expansion as the sleeve member 35, together with therounded end surface construction thereof, substantially prevents anyinward component of force that resists expansion of the ends of thesleeve member 35 such as might occur for example, between two slidingsurfaces were the thrust rings 58 and 59 to engage the ends of thesleeve member 35 directly. 7

Each of the resilient structures 33 and 34 can be adjustably positionedwithin the housing in order to selectively adjust the required trippingforce. As disclosed in full detail in application, Ser. No. 82,285,Nutter, filed concurrently herewith and assigned to the assignee of thepresent invention, this is accomplished by providing upper and lowerjack mandrels 85 and 86, each having an end portion adapted to engagethe outermost tube 68 of the respective resilient structures 33, 34.Each jack mandrel is threaded to the housing at 87 so that relativerotation will cause feeding thereof along the housing 20. Suitablewindows 88 are provided in the wall of the housing 20 adjacent to thedistal end section of each jack mandrel, the windows being normallyclosed by plugs 89. Removal of the plugs 89 provides access openingsthrough which a suitable tool (not shown) can be inserted and engaged incircumferentially spaced recesses 90 and used to rotate the jack mandrelwith respect to the housing 20. Such rotation causes the threads 87 tofeed the jack mandrel along the housing in one direction or the other,depending upon the direction of rotation, to correspondingly change theamount the resilient structures 33 and 34 must be foreshortened in orderto position the release grooves 48 opposite the outer sleeve memberthreads 47. Since the required tripping force is a direct function ofthe amount of longitudinal deflection of the resilient structures 33 and34, the tripping force can be adjusted as desired. A stop plug 91 havinga tang 92 that projects into one of a plurality of circumferentiallyspaced external grooves 93 on the jack mandrel is of course removedduring rotation and is then engaged to lock the jack mandrel in theselected longitudinal position by preventing rotation thereof.

To prevent relative rotation of the various parts'of the trippingmechanism 32 and thereby maintain the proper alignment of the threadsand the locking surfaces during operation as well as the slots in thesleeve member35 and thrust sleeves 79 for proper expansion duringoperation, a system of keys is used as shown more clearly in FIGS. 4 and5. The sleeve member 35 can have, for example, sixteen slots (eightopening in each direction as shown in FIG. 3) with the mandrel 21 andthe release sleeve 45 each having eight radially aligned keywaysprovided by longitudinally extending grooves 95 and 96. In this example,each of the thrust sleeves 79 also has eight slots 81 extending in eachdirection. Thus the upper thrust sleeve can have its downwardly openingslots longitudinallyaligned with the upwardly opening slots in thesleeve member 35, and a series of elongated keys are provided, eachextending into the aligned slots. The inner edge of each key 100 ridesin a respective mandrel keyway 95, whereas the outer edge is received bythe radially aligned keyway 96 in the locking sleeve 45. A separate setof shorter keys 101 ride in the same mandrel keyways 95 and extend intoslots of the lower thrust sleeve so that the upwardly opening slots inthe lower thrust sleeve are longitudinally aligned with the downwardlyopening slots 42 in sleeve member 35. Also upper and lower sets of shortkeys 102 and 103 are received in radially extending slots 104 and 105cut in the drive rings 58 and 59 and ride in the mandrel keyways 96 torotatively position the drive rings and thus the locking sleeve 44 withrespect to the mandrel 21 and the sleeve member 35. Accordingly, therelease threads 36 and 37 and the locking surfaces 43 and 46 are fixedrotationally for the proper meshing relationship, and the slots thatenable expansionof the sleeve member 35 and the thrust sleeves 79 areproperly aligned for opening and closing movement during such expansion.

In operation, the jar 13 in its fully open or extended condition isconnected in the drill string above the drill collars 12 and loweredinto the borehole for drilling operations. During drilling, rotarymotion is transmitted through the jar 13 by virtue of theinterengagement of the splines 29, and during normal operations the jaris always in tension. In case the tools below the jar 13 become stuck,the jar is operated as follows. The drill pipe is lowered until arestraint is seen on the rig weight indicator which means that thetripping mechanism 32 is in the cocked position as shown in FIG. 2B. Tohit upwardly, an upward strain is applied to the drill pipe 14 at thetop of the borehole, causing the string to stretch and store energy. Theupward force will tend to pull the housing 20 upwardly relative to themandrel 21, however such upward movement is resisted by the resilientstructure 34 disposed between the lower jack mandrel 86 and the lowerdrive ring 59, which is held against'upward movement by the sleevemember 33 and the thrust sleeve 79. The upward force on the sleevemember 35 and the threads 36 and 37, due to their inclined wall surfacesof the latter, will tend to cause expansion of the sleeve member;however the top or crest surfaces 43 and 46 lock the sleeve member ingripping engagement with the mandrel 21. As the where the releasegrooves 48 are positioned laterally opposite the threads 47. At thispoint, which corresponds to a predetermined tripping or release force,the inclined walls of the threads 36 and 37 will cause the sleeve member35 to expand outwardly and suddenly release the gripping engagement withthe mandrel 21. The housing will be accelerated upwardly,

. causing the hammer surface to strikethe anvil surface 26 in a violentmanner. The impact force is transmitted via the mandrel 21 to the stucktools ther'ebelow. As the sleeve member shifts upwardly drel 21. Whenthe sleeve member 35 arrives opposite the threads 37 it will contractinto gripping engagement the reaction force of the deflected structure34 which is translated to radial inward force components by the inclinedwall surfaces 49 of the release grooves 48. The mandrel portions 60' and61 coact with the internal configuration of thesleeve member 35 andfunction in such a manner that there is only one longitudinal positionwhere the sleeve member can contract, thus minimizing thread wear.

Jarring blows can be applied repeatedly in an upward direction, ordownward jarring can be effected by slacking off the weight of the drillpipe onto the jar housing 20. The same coaction of parts will occur as Idescribed above except involving the upper resilient V 37 as thegripping means between the sleeve member 35 and the mandrel 21 minimizeswear on the parts.

This is because the maximum stress on the threads'36 "and 37 is directlyproportional to the contact pressure and inversely proportional to thetotal length of contact surface. In order to keep the maximum stresswithin values which will minimize wear, it is important to proforexample, by eliminating the upper resilient struc- I ture, jack mandreland associated structure and'cor respondingly shortening the housing andthe mandrel.

Since certain changes or modifications may be made in the disclosedembodiment without departing from the inventive concepts involved, it isthe aim of the appended claims to cover all such changes and modifications falling within the true. spiritand scope of the with the mandrel21, such contraction being assisted by member vide the longest possiblecontact surface, which the threads 36 and 37 do provide as opposed toother structure such as parallel ribs or the like. Moreover, threads canbe conveniently formed for the proper full length contact withconventional tooling. The thrust sleeves 79 having rounded end surfacesengaging the annular grooves in the ends of the sleeve member 35practically invention is illustrated in connection with a two-wayhitting jar (both upward and downward), it will be appreciated that thejar could be readily modified to an embodiment that hits only in onedirection, upwardly present invention.

I claim:

1. A well jar apparatus comprising: inner and outer memberstelescopically related and having impactsub' faces that can be engaged;by telescoping motion to deliver a jarring blow to an object that isstuck in a well bore; a tripping mechanism'for preventing substantialtelescoping motion of saidmembers until a predetermined longitudinaltripping force is applied to said members including an expansible andcontractible sleeve member surrounding said innermember; axial cam meansformed in an external surface of said inner member and adapted to meshwith companion :cam means formed in an internal surface of said sleevefor providing gripping engagement therebetween and for causing expansionof said sleeve Y member, said cam means being arranged to providecontinuous bearing contact=surfaces which are considerably longer thanthe outside circumference of saidinner member in order to distribute the.stress on said. cam means in such a manner as to minimizewear thereondue to'repeated engagement under high load conditions; and means forpreventing relative rotation between said sleeve member and said innermember.

deliver a jarring blow toan object that is stuck in a well bore; anexpansible sleeve member contracted'around said inner member andhavinginternal threads that mesh with external threads formed in an outersurface of said inner member to prevent relative longitudinal movement,said threads having inclined wall surfaces adapted to expand said sleevemember outwardly; locking means released by a predetermined amount oflongitudinal movement of said outer member relative to said sleevemember for preventing expansion of said sleeve member; resilient meansfor resisting longitudinal movement of said housing member with areaction force that is a function of the-amount of such longitudinalmovement, release of said locking means enabling expansion of saidsleeve member and disengagement of said threads, whereby said memberscan telescope freely to'bring said impact surfaces together in a violentmanner; and radially disposed means for preventing relative rotationbetween said sleeve member and said inner member.

4. The well jar apparatus of claim 3 wherein said sleeve member hasslots extending in alternating longitudinal direction for less thanthefull length thereof I to divide said sleeve member into a plurality ofsegments with the ends of each segment being joined to an end of anadjacent segment.

5. The well jar apparatus of claim 4 wherein said radially disposedmeans includes at least one key extending through a slot in said sleevemember and having its inner edge slidably disposed in a groove extendinglongitudinally in the periphery of said inner member.

6. A well jar apparatus comprising: inner and outer telescopicallyrelated members adapted for connection in a pipe string and havingimpact surfaces that can be brought together by telescoping movement todeliver a jarring blow to an object that is stuck in a well bore; anexpansible sleeve member contracted around said inner member and havinginternal threads that mesh with external threads formed in an externalsurface portion of said inner member to prevent relative longitudinalmovement, said threads having inclined wall surfaces adapted to expandsaid sleeve member outwardly; locking means released by a predeterminedamount of longitudinal movement of said outer member relative to saidsleeve member; and resilient means disposed in opposition to saidlongitudinal movement and yieldably resisting such longitudinal movementwith a reaction force that is a function of the amount of suchlongitudinal movement, said resilient means comprising a tubular columnstructure having a plurality of concentrically disposed tubes and beingcapable of longitudinal deflection, release of said locking meansenabling expansion of said sleeve member and disengagement of saidthreads, whereby said members can telescope freely to bring said impactsurfaces together in a violent manner.

7. The well jar apparatus of claim 6 wherein said plurality ofconcentrically disposed tubes have ends coupled in such a manner thatlongitudinal force applied to one of said tubes places alternate tubesin tension and compression.

8. The well jar apparatus of claim 6 wherein said plurality ofconcentrically disposed tubes comprises an outer tube coupled to saidouter member, an inner tube coupled to said sleeve member and anintermediate tube disposed between said inner and outer tubes, saidintermediate tube having a first outwardly extending shoulder that isengaged by one end of said outer tube and a second inwardly extendingshoulder that is engaged by one end of said inner tube, wherebylongitudinal force applied to said outer tube places said outer tube andsaid inner tube in compression and said intermediate tube in tension.

9. The well jar apparatus of claim 8 wherein the other respective endsof said inner and outer tubes extend beyond the adjacent ends of saidintermediate tube.

10. In a well jar apparatus having inner and outer memberstelescopically disposed and a releasable tripping mechanism forresisting telescoping movement, said tripping mechanism being releasedby longitudinal movement of one of said members, resilient meansdisposed in opposition to said longitudinal movement and includingconcentrically disposedtubes having ends coupled in such a manner thatlongitudinal force tending to cause telescoping movement in oppositedirections of said inner and outer members places alternate tubes incompression and tension.

1 1. A well jar apparatus comprising: inner and outer memberstelescopically related and having impact surfaces at can engaged bytelescoping motion to deliver a jarring blow to an object that is stuckin a well bore; an expansible sleeve member contracted around said innermember and having gripping engagement therewith; cam means responsivetolongitudinal force on said sleeve member for expanding said sleevemember radially outwardly; releasable locking means for preventingexpansion of said sleeve member until a predetermined tripping force isapplied to said members; resilient means coupled between one of saidmembers and said sleeve member for resisting longitudinal relativemovement; and means including an annular member disposed between saidresilient means and said sleeve member and having an end surface inbearing contact with said sleeve member for substantially isolating saidsleeve member from radially inward force components during expansion ofsaid sleeve member.

12. The well jar apparatus of claim 11 wherein said end surface isrounded and rolls during expansion within an annular concave grooveformed in the end of said sleeve member.

13. The well jar apparatus of claim 12 wherein said annular member isconstituted by a plurality of adjacent segments having the capabilityfor expansio with said sleeve member.

1. A well jar apparatus comprising: inner and outer memberstelescopically related and having impact surfaces that can be engaged bytelescoping motion to deliver a jarring blow to an object that is stuckin a well bore; a tripping mechanism for preventing substantialtelescoping motion of said members until a predetermined longitudinaltripping force is applied to said members including an expansible andcontractible sleeve member surrounding said inner member; axial cammeans formed in an external surface of said inner member and adapted tomesh with companion cam means formed in an internal surface of saidsleeve member for providing gripping engagement therebetween and forcausing expansion of said sleeve member, said cam means being arrangedto provide continuous bearing contact surfaces which are considerablylonger than the outside circumference of said inner member in order todistribute the stress on said cam means in such a manner as to minimizewear thereon due to repeated engagement under high load conditions; andmeans for preventing relative rotation between said sleeve member andsaid inner member.
 2. The well jar apparatus of claim 1 wherein saidaxial cam means are provided by stub threads having flat top surfacesand inclined side wall surfaces.
 3. A well jar apparatus comprising:inner and outer members telescopically related and having impactsurfaces that can be engaged by telescoping motion to deliver a jarringblow to an object that is stuck in a well bore; an expansible sleevemember contracted around said inner member and having internal threadsthat mesh with external threads formed in an outer surface of said innermember to prevent relative longitudinal movement, said threads havinginclined wall surfaces adapted to expand said sleeve member outwardly;locking means released by a predetermined amount of longitudinalmovement of said outer member relative to said sleeve member forpreventing expansion of said sleeve member; resilient means forresiSting longitudinal movement of said housing member with a reactionforce that is a function of the amount of such longitudinal movement,release of said locking means enabling expansion of said sleeve memberand disengagement of said threads, whereby said members can telescopefreely to bring said impact surfaces together in a violent manner; andradially disposed means for preventing relative rotation between saidsleeve member and said inner member.
 4. The well jar apparatus of claim3 wherein said sleeve member has slots extending in alternatinglongitudinal direction for less than the full length thereof to dividesaid sleeve member into a plurality of segments with the ends of eachsegment being joined to an end of an adjacent segment.
 5. The well jarapparatus of claim 4 wherein said radially disposed means includes atleast one key extending through a slot in said sleeve member and havingits inner edge slidably disposed in a groove extending longitudinally inthe periphery of said inner member.
 6. A well jar apparatus comprising:inner and outer telescopically related members adapted for connection ina pipe string and having impact surfaces that can be brought together bytelescoping movement to deliver a jarring blow to an object that isstuck in a well bore; an expansible sleeve member contracted around saidinner member and having internal threads that mesh with external threadsformed in an external surface portion of said inner member to preventrelative longitudinal movement, said threads having inclined wallsurfaces adapted to expand said sleeve member outwardly; locking meansreleased by a predetermined amount of longitudinal movement of saidouter member relative to said sleeve member; and resilient meansdisposed in opposition to said longitudinal movement and yieldablyresisting such longitudinal movement with a reaction force that is afunction of the amount of such longitudinal movement, said resilientmeans comprising a tubular column structure having a plurality ofconcentrically disposed tubes and being capable of longitudinaldeflection, release of said locking means enabling expansion of saidsleeve member and disengagement of said threads, whereby said memberscan telescope freely to bring said impact surfaces together in a violentmanner.
 7. The well jar apparatus of claim 6 wherein said plurality ofconcentrically disposed tubes have ends coupled in such a manner thatlongitudinal force applied to one of said tubes places alternate tubesin tension and compression.
 8. The well jar apparatus of claim 6 whereinsaid plurality of concentrically disposed tubes comprises an outer tubecoupled to said outer member, an inner tube coupled to said sleevemember and an intermediate tube disposed between said inner and outertubes, said intermediate tube having a first outwardly extendingshoulder that is engaged by one end of said outer tube and a secondinwardly extending shoulder that is engaged by one end of said innertube, whereby longitudinal force applied to said outer tube places saidouter tube and said inner tube in compression and said intermediate tubein tension.
 9. The well jar apparatus of claim 8 wherein the otherrespective ends of said inner and outer tubes extend beyond the adjacentends of said intermediate tube.
 10. In a well jar apparatus having innerand outer members telescopically disposed and a releasable trippingmechanism for resisting telescoping movement, said tripping mechanismbeing released by longitudinal movement of one of said members,resilient means disposed in opposition to said longitudinal movement andincluding concentrically disposed tubes having ends coupled in such amanner that longitudinal force tending to cause telescoping movement inopposite directions of said inner and outer members places alternatetubes in compression and tension.
 11. A well jar apparatus comprising:inner and outer members telescopically related and having impactsurfaces that can be engaged by teLescoping motion to deliver a jarringblow to an object that is stuck in a well bore; an expansible sleevemember contracted around said inner member and having grippingengagement therewith; cam means responsive to longitudinal force on saidsleeve member for expanding said sleeve member radially outwardly;releasable locking means for preventing expansion of said sleeve memberuntil a predetermined tripping force is applied to said members;resilient means coupled between one of said members and said sleevemember for resisting longitudinal relative movement; and means includingan annular member disposed between said resilient means and said sleevemember and having an end surface in bearing contact with said sleevemember for substantially isolating said sleeve member from radiallyinward force components during expansion of said sleeve member.
 12. Thewell jar apparatus of claim 11 wherein said end surface is rounded androlls during expansion within an annular concave groove formed in theend of said sleeve member.
 13. The well jar apparatus of claim 12wherein said annular member is constituted by a plurality of adjacentsegments having the capability for expansion with said sleeve member.